perf(resolution): fix O(K²) import-node blowup in "Resolving refs" (#915) (#965)

* perf(resolution): resolve imports to definitions, not sibling import nodes (#915)

"Resolving refs" crawled (tens of minutes) on large projects — most painfully
ones mixing a big front-end and back-end. An external package or module imported
across hundreds/thousands of files (react, a shared UI package, Python
logging/typing) is re-declared as an `import` node in every importing file, so
its unresolved import ref fell through to the exact-name matcher, which scored
all K same-named import nodes via findBestMatch — K refs x K candidates = O(K^2)
per package, producing only meaningless import->import edges.

Fix: exclude `import`-kind nodes as name-match targets (they're statements, not
definitions; real import->definition resolution is the import resolver's job).
Plus two safe constant-factor wins in findBestMatch: hoist the per-candidate
ref.filePath split, and skip cross-language candidates when a same-language one
exists (provably the same winner — same-language scores >=50, cross-language
maxes at 35).

Measured: superset (Py+TS) candidates scored 7.5M -> 833K (9x), non-import edges
preserved (+1618 now resolve to real defs), ~22K useless import->import edges
removed; kubernetes (Go) computePathProximity 37.2s -> 5.0s; synthetic 8k-file
mixed repo (K=4000) resolution 16.0s -> 1.7s. Full suite green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs: correct stale better-sqlite3/wasm references to node:sqlite

The SQLite backend has been Node's built-in node:sqlite (real SQLite, WAL + FTS5,
from the bundled runtime) for a while — there is no native build step and no
node-sqlite3-wasm fallback. README and the docs site were already updated; this
catches the stragglers:

- CLAUDE.md: the src/db/ backend description and the sqlite-backend test note.
- src/db/index.ts, src/mcp/tools.ts: two code comments that still blamed "the
  wasm backend" for non-WAL behavior (reworded to "when WAL isn't in effect").

Leaves tree-sitter grammar wasm (web-tree-sitter / --liftoff-only) untouched —
that's a different, still-current use of wasm.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(telemetry): drop the dead sqlite_backend field (schema v2)

node:sqlite is now the only backend, so the `index` event's `sqlite_backend`
field was a constant ("native") carrying no signal — and the `install` event
never actually sent it. Remove the field and the backendKind() helper, bump the
telemetry SCHEMA_VERSION 1 -> 2, and update TELEMETRY.md + docs/design/telemetry.md.

The ingest worker is deliberately left tolerant: `index` doesn't require the
field and schema_version validates as nonNegInt(99), so v2 events ingest fine and
old clients still sending v1 + sqlite_backend keep validating too. Added a legacy
comment there explaining it's safe to drop once old-client share is negligible.

telemetry.test.ts: the assertion pinning schema_version and a stale-claim fixture
line updated 1 -> 2. All telemetry tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/design/telemetry.md

@@ -20,7 +20,7 @@ Answer, in aggregate and anonymously:
 - Which install targets people pick, local vs global, fresh vs upgrade.
 - Which MCP tools and CLI commands get used, how often, and how often they error.
 - Which languages people index (prioritize extractor/framework work by real usage).
-- Version adoption speed, OS/arch/Node mix, native-vs-wasm SQLite backend share.
+- Version adoption speed, OS/arch/Node mix. (The SQLite backend is always the built-in `node:sqlite` now — there is no native-vs-wasm split left to measure.)
 
 ## Non-goals / never collected
 
@@ -63,11 +63,10 @@ Common envelope on every batch (computed once per process):
 Event types:
 
 - **`install`** — one per installer run. Props: `targets` (e.g. `["claude","cursor"]`),
-  `scope` (`local`/`global`), `kind` (`fresh`/`upgrade`/`reinstall`), `sqlite_backend`
-  (`native`/`wasm`).
+  `scope` (`local`/`global`), `kind` (`fresh`/`upgrade`/`reinstall`).
 - **`index`** — one per full index (`init`/`index`, not per `sync`). Props: `languages`
   (names only, e.g. `["typescript","go"]`), `file_count_bucket` (`<100`, `100-1k`, `1k-10k`,
-  `10k+`), `duration_bucket` (`<10s`, `10-60s`, `1-5m`, `5m+`), `sqlite_backend`.
+  `10k+`), `duration_bucket` (`<10s`, `10-60s`, `1-5m`, `5m+`).
 - **`usage_rollup`** — the workhorse. One event per `(day, kind, name)` per machine,
   aggregated locally. Props: `kind` (`mcp_tool`/`cli_command`), `name`
   (e.g. `codegraph_explore`, `affected`), `count`, `error_count`, and for MCP: